Abstract
An experimental investigation was carried out to study the potentials of oyster shell ash (OSA) to be used as supplementary cementitious material (SCM) exposed to sulphuric acid environment. Experiments were carried out by supplementing 5 – 20 % of OSA by weight of cement in concrete. The mix ratio used was 1:2:4 (binder, sand and granite) with water cement ratio maintained at 0.5. A total of 320 cube specimens (150mm x 150mm x 150mm) were cast and tested for compressive strength at 7, 14, 21 and 28 days of curing in potable tap water and (5, 7.5 and 10 %) sulphuric acid solutions. It has been deduced that the compressive strength of concrete specimen progressively increased with longer curing periods and decreased with OSA content for specimen immersed in water whereas for specimen immersed in sulphuric acid solutions the compressive strength decreased with longer curing period, OSA content as well as sulphuric acid content. Generally, results of the statistical analysis showed that sulphuric acid concentrations, OSA contents and curing periods have significant effect on the compressive strength of concrete. The use of OSA as SCM did not mitigate the adverse effects of sulphuric acid on the compressive strength of cement blended with OSA. Keywords: Compressive strength, Oyster shell ash, Statistical analysis, Sulphuric acid environment, supplementary cementitious material DOI : 10.7176/CER/11-4-07 Publication date :May 31 st 2019
Highlights
Concrete is a durable material with little or no maintenance except when it is exposed to aggressive surroundings (Shetty, 2009)
The principal objective of this study is to evaluate the compressive strength of oyster shell ash (OSA)-cement concrete placed in water and 5, 7.5 and 10 % H2SO4 acid concentration
The sand satisfies the requirement of lower and upper limits of the percentage by mass passing as specified by BS 882 (1992). It could be observed from the grading curves that the Coefficient of uniformity (Cu) and Coefficient of curvature (Cc) for the fine aggregates are 1.87 and 1.14 respectively
Summary
Concrete is a durable material with little or no maintenance except when it is exposed to aggressive surroundings (Shetty, 2009). Sulphate attack is one of the most destructive surroundings that influence the mechanical and physical properties of concrete structures. The reaction of sulphate ions with calcium hydroxide and calcium aluminate hydrate to form ettringite and gypsum had been reported by (Nabil, 2016; Salah, 2007). They concluded that these products (ettringite and gypsum) lead to cracking, deterioration, expansion and deformation of hardened concrete structures. Several researchers are in agreement to the fact that acids have a profound effect on the strength and other properties of concrete (Zivica and Bajza, 2001: Turkel et al 2007)
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